A mobile device such as a mobile phone and a tablet computer can provide various functions (e.g., via applications installed in the mobile device) such as taking/viewing pictures, playing music and movies, playing games, sending/receiving emails and message, etc., to the user. Besides, a size and power consumption of the mobile device have been continuously and significantly reduced due to modern advancement of semiconductor technologies. Thus, the mobile device has become a daily and essential appliance carried by a user.
However, even though design of the mobile device is greatly improved nowadays, hardware buttons and hardware controllers are necessarily installed in the mobile device. That is, the hardware buttons and the hardware controllers are still necessary for controlling functions of the mobile device, e.g., volume, applications and camera. Accordingly, thickness of the mobile device can not be further reduced, and convenience of the mobile device is limited. Therefore, how to execute the functions without needs of the hardware buttons and the hardware controllers is a topic to be discussed.